Classifying process and apparatus



Aug. 22, 1944. J. A. BRUssET CLASSIFYING PROCESS AND APPRATUS Filed Oct.l, 1941 3 Sheets-Sheet l Jean/lbert Brusse.

Aug. 22, 1944. J A BRUSSET l2,356,648

CLASSIFYING PROCESS AND APPARATUS Filed Oct. 1, 1941 '5 Sheets-Sheet 2Aug. 22, 1944. J. A. BRUssE'r CLASSIFYING PROCESS AND APPARATUS FiledOct. 1, 1941 3 Sheets-Sheet 3 Syvum/vbo@ Jean, .Hilbert Brussel:

Patented Aug. 22, 1944 UNITED STATES PATENT OFFICE 2,356,648 cLAssIFYINGPaooEss AND APrARA'rUs Jean Albert Brusset, Blairmore, Alberta, CanadaApplication October 1, 1941, Serial No. 413,218

8 Claims.

The present invention relates to processes and apparatusfor separatingmixed granular materials of difierent specific gravities according totheir specific gravities, and particularly into three or more clean-cutproducts, by means of a novel flotation bath made up 'of a suspension ofsolid materialin water. i

It has in the past been found relatively easy f to make two-productseparations, (one oat," and one sink) in liquids or suspensions. Inattempts to split the sink into two further products oi' differentspecic gravities the prior investigators attempted to effect the furtherseparation by creating rising currents in the bath, it having been thetheory that such currents would have more lifting action on the lightermaterial in the sink, and would be expected to carry this lightermaterial away to a convenient means of gathering and conveying. However,it

has been found that this theory does not Workout in practice, becausethese currents select, -among the particles of the sink, not only thoseparticles of lesser specific gravity but also those of smaller sizeregardless of specific gravities which oier a relatively greater surfaceto the action of those currents. The result is that the material carriedoi by such accessory currents is a mixture of large and small particlesof material of intermediate specic gravity, plus small particles of theheavier specific gravity material. Conversely, there remain in theheavier material, separated as tailings ,-or lrefuse, the largerparticles of the intermediate material. Thus a clean-cut separation ofthe sink" into "intermediate and tailing or refuse has not been possiblewith prior processes using accessory currents. to divide the sink Theprocess of the present invention eliminates the use of any currents inthe bath for the selection of refuse and middlings, and thus avoids thedanger of impure products, as will be seen below.

A primary object of the invention is to obtain a perfect separation ofthree very clean-cut products (concentrate, middlings and tailings, or,in the case of coal, clean coal, middlings and refv use) by the use ofone unique bath, of appropriate specic gravity, of a suspension of inelydivided solid material in water.

An important object of the invention is the provision of an improvednovel flotation medium for the separation of a mixture of materials ofdiierent specic gravities by a sink and oat process.

It is an object of the invention, also, to vprovide novel apparatus foruse in eecting this sink and oat process.

The new flotation medium of the. invention consists essentially of anaqueous suspension of finely divided limestone rock, minus 150 mesh, insuiiicient concentration-to provide al medium y,of required'speciiicgravity. The limestoriev rock should be as pure as possible, that is,especially free from shales and clay. Ground limestone rock makes verystable suspensions in water, and all specific gravities of flotationmedium, between, 1.30 and 1.70, can readily be provided without undueviscosity oi the medium at the higher values. Y

By grinding the limestone sothat 90% passes a mesh screen there is asmall percentage of larger particles which settle more rapidly, thusmaintaining a slightly higher specific gravity of medium adjacent thebottom of the bath, which circumstance is an advantage in the presentprocess as it expedites separation of the sink into two final products.

Finely divided limestone rock as the solid ingredient of the suspensionmedium possesses a number of advantages over previously proposed media:thus, it is readily available almot everywhere; it is easily crushed tothe required mesh; it is not abrasive on the machinery; it remainsreadily in suspension; it does not stick to the finished products `andis easily washed off of them; and it is easily recovered from the washwater by cycloning so that recycling is facilitated.

In' one aspect, the process of the present invention consistsessentially `in introducing a mix-` ture of solid particles of lighterand heavier specific gravities into a bath of they aqueous suspension ofiinely divided limestone' having a density adjusted to float the lighterbut not the heavier particles, and separately removing lighter particlesfrom the top and heavier particles from the bottom of the bath.

I have found that said nely divided limestone suspension may be used asthe suspension medium in a modification of the aforesaid process, bywhich a mixture of lighter, intermediate, and heavier particles can beseparated into its components, as follows: The density of the bath ofsuspension mediumie. g., Iaqueous suspension of finely dividedlimestone) is so adjusted that the light particles iloat thereon whilethe intermediate and heavy particles sink therein at varying rates ofspeed (preferably, s0 adjusted that the intermediate particles sink onlyvery slowly through the bath): after the heavy particles have lsunkthrough a substantial depth of the `bath there is imparted to themastep-by-step translational movement, to one side or end of thecontainer, by means of a longitudinally reciprocating sloping steppeddeck (preferably, a longitudinally reciprocating sloping stepped deckwhose forward motion, in the direction of the upper end thereof, isslower than its backward motion), whereby the sunken heavy particles arecollected substantially at one line (i. e., the top end of the steppeddeck) at which line the socollected heavy particles are separatelywithdrawn from the container and suspension. The intermediatessimultaneously are concentrated at the low end of the stepped deck andare continuously or intermittently withdrawn, admixed with suspensionmedium, at the latter. The light particles are, of course, separatelywithdrawn at the top of the bath of suspension medium.

While the aforesaid aqueous suspension of finely divided limestone isadmirably suited for use in the 3-way separation just described thelatter may be carried out with the use of one or another of the priorart suspension media.

After the removal of the separated components, the latter are washed toremove suspension medium therefrom, and the suspension medium isreformed for reuse in a repetition of the process. From the viewpoint ofthe suspension medium, the 3-way separation process is a cyclical one,in which the steps constituting one cycle are as follows:

l. Suspension medium, of controlled predetermined density is fed to aseparatory vessel to maintain therein a bath of predetermined depth;

2. Suspension medium, plus separated particles of the mixture undergoingtreatment, is removed from the bottom of the separatory vessel;

3. Withdrawn suspension medium is removed from said separated particlesby washing, thereby producing diluted suspension medium;

4. The so-diluted suspension medium is partially dewatered (theresulting water being use'- ful for the Washing step 3);

5. Fresh suspension medium of predetermined density is reformed from thedewatered suspension obtained 'in step 4 plus additional water, and usedas the suspension medium in step 1.

In step 3 of the -cyclical process, the with? drawn material is washedin a plurality of stages,

in the first of which I employ as washing liquid the water obtained bypartially dewatering the diluted suspension medium which is the productof that step; in a second stage of which I employ as washing liquidfiltrate from the said ,water; and in the final stage of which I employas washing liquid fresh make-up water. The three wash waters arecombined and in step 4, are partially dewatered by treatment in acyclone separator yielding (a) thickened suspension medium and (b) awater contaminated with a relatively small amount of the solids of theoriginal suspension medium; which latter is divided into two portionsone of which is used as initial washing liquid and the other of which isfurther clarified by filtration for use as intermediate washing liquid.The filter cake, consisting essentially of solids of the originalsuspension medium, may be and preferably is added to the thickenedsuspension medium obtained from the cyclone separator.

In carrying out step 5 of the cyclical process, I feed streams ofthickened suspension medium and water (specifically, the partiallyclarified wa# ter from'the cyclone separator) to a mixing vessel,continuously automatically determine the specific gravity of theresulting mixture, and continuously automatically control the rates offeed of thickened suspension medium and water to said mixing tank tomaintain the specific gravity of the mixture within narrow predeterminedlimits, as will be described more fully hereinafter.

The process and apparatus used in practicing the same will be describedin greater 'detail with reference to the accompanying drawings whichillustrate a preferred embodiment of the invention and in which:

Fig. 1 is a diagrammatic view of a plant embodying the invention;

Fig. 2 is a vertical sectional view of the main separating tank;

Fig. 3 is a sectional view approximately on the line 3-3 of Fig. 2;

Fig. 4 is an enlarged diagrammatic view of the suspension feed controls,and

Fig. 5 is a detail of the mounting of the submerged deck.

The main classifying tank 5, which will vary in size depending on thecapacity desired, preferably is a metaltank having at one end a feed bin6 which discharges onto a slanting feeding shelf 1 and disposed at anangle of about 30 at its lower end within the tank 5. An endless rakingconveyor 8, running over sprockets 9 and I0 mounted at opposite ends ofthe tank, rakes the mixed material oi Aof the feed shelf 'I as the rakesII of the lower flight thereof begin their travel through the tank, andconveys the lighter materials which iioat on the separating medium tothe other end and out over a discharge lip I2 at the end opposite thefeed bin 6. The rakes II of the conveyor are made of perforated sheetiron and travel at a slow rate of speed through the upper portion of thebath so that they cause no undue agitation which might result inimperfect separation.

The heavy and intermediate materials of the mixture supplied throughfeed bin E sink through the bath between the lower edge of feed plate l.

' and an inwardly slanting defiecto'r plate I 3' mounted on the insideof tank wall il opposite plate 1 to a reciprocating deck or screen i5.The deck I5 is mounted at an angle of about 5 to 10 to the horizontalwith its lower end beneath the plate 1, the amount of the slope beingdependent on the characterl of the material being separated, and issupported on arms I6 which y are set perpendicular to the plane of thedeck so that the motion of the deck is practically longitudinal in itsown plane without any appreciable vertical or jigging component.

The upper .ends of the supporting arms for the reciprocating deck I5terminate ina spindle I 1 upon which is mounted a heavy block or bushingI8 of rubber clamped between plates I9 by a nut 20. Steel collars 2|carried -on depending brackets 22 secured to the side frames 23 of thedeck I5, clamp the rubber bushings I8 to make the connectionbetween thearms and the deck. Similar rubber blocks or bushings 24 mounted on thelower ends of the arms I6 are clamped between collars 25 carried onbrackets 26 secured to a stationary member 28 mounted between the sidewalls of the tank 5. When the deck I5 is reciprocated by the meansdescribed hereafter the rubber blocks or bushings I8 and 24 yieldsufficiently to allow the motion of the screen to take place and act asbearings not requiring lubrication. This is important because `all ofthese parts are immersed in the suspension medium.

Reciprocating motion is imparted to the deck I5 by a drive rod 29 whichextends through the end wall 30 of the tank, its passage and motiontherethrough being sealed by a rubber diaphragm 3I. The inner end of therod 29 is provided with a rubber bushing 32 which is clamped by a collar33 carried by a bracket 34 fastened to the deck I5. A roller 35 mountedon the outer end of the rod 29 bears on a rotary cam 36, the

profile of which is formed so as to advance the deck slowly toward itsupper end and permit a `l drives. Worm-conveyor 43 also collects andconquick return motion. The quick return motion of the deck is partiallycaused by the resilience of the rubber block connections at the ends ofthe supporting arms and in addition is effected by resilient coilsprings 31 acting between the upper end of the upper set of arms I6 anda stationary part of the tank 5. The driving cam 36 for impartingreciprocating motion to the deck is driven at the rate of about 120revolutions a minute.

The supporting surface of the deck I is preferably formed of sheet ironperforated uniformly over its area with A or 1/2 inch holes` 38 and iscorrugated or crimped into stepped formation to provide upwardly slopingsteps 39 terminating in steep faces or shoulders 40 which face towardthe upper end of the deck. The upper end of the deck extendsbeneath thelower end of the deflector plate I3 and terminates over the upper end ofa discharge channel 4I. The lower end of the deck I5 extends to a pointadiacent the wall 39 under the plate 1 and over the edge of a dischargechannel 42.

In the course of operation, the lighter material, or fioat, is evacuatedfrom the box by conveyor 8 over the lip I2. The heavier material sinksbetween plates 1 and I3 and toward deck I5. The lighter portion of thatmaterial, or middlings, which has a specific gravity fairly close tothat of the bath, sinks more sluggishly than does the heavier material,which latter tends to reach and rest upon the deck I5. Due to the factthat the deck I5 moves quickly rearwardly, that is, in the direction ofthe lower end thereof, the heavy material will, because of its inertia,slide forward along the slightly inclined upper faces 39 of the steps,but during the forward and slower motion of the deck, the steep faces 40of the steps will catch the heavy material and advance it toward theupper end of the deck. The heavy material will thus move step by steptowards plate I3 along the deck, and finally will be discharged from theupper end of the de'ck into passage 4I under plate I3.

The intermediate particles or middlings," the gravitational motion ofwhich is too sluggishin the heavy mediumto cause the same to be h eld incontact with the stepped screen, will move in the opposite direction,that is to say, towards veys whatever small heavy particles of materialhave fallen through the perforations of decl: I5, and the portion of thesolid medium which has slowly settled to thebottom of the separatingtank 5. v

As may be seen from the above, the separation of the mixture into threeproducts does not make use of any currents whatever. 'I'he onlyprinciples involved are those of sink-and-fioat separation in a bath ofappropriate specific gravity, plus separation of the sinks into twoproducts by selective fricticnal action of the reciprocating steppeddeck on the heavier particles of the sin The clean coal discharged overthe lip I2, the middlings discharged into the channel 42 and the refusedischarged into the channel 4I together with the fine heavy material andsettled suspension which iinds its way into channel 41 are delivered bysuitable conveyors 46--46, 46 and 45, respectively, to washing screens49, which for convenience are preferably arranged side by side. As theseparated materials pass over the screens 49 they are washedsuccessively by water from other stages of the process and finally lbyclean make-up water supplied through sprays 50, 5I and 52, respectively.

The spent wash water with the medium washed from the separated materialson screens49 is caught by collectors 53 beneath the screens and flowstherefrom to a tank 54. A pump 55 delivers the dilute suspension fromtank 54 through pipe 56 tangentially at high speed into a cycloneseparator 51 where thebulk of the solids of the sus- .;r, pension mediumare separated from the wash medium to tank 54, small quantities offlotation 'n y reagents (oil in the case of coal) and air are by meansof injector 58 continuously injected into the right-hand side of thetank 5, under the influence of gravity alone, since the right-end of thedeck is lower than the left end. The loosening of the mass of middlingsby the motion of the screen will accelerate this displacement under theinfluence of gravity. The middlings travel past the lower end of thedeck I5 and are deposited in a transverse channel 42, the edge of whichis overlapped by the end of the deck.

It will be seen that as the specific gravity of the suspension ispractically equal to that of the middlings, the latter are subjected toa resultant force which is practically nil; so that if they pipe 56between pump 55 and the cyclone separa- `tor 51 to produce in thecyclone a flotation reaction which causes the entrained particles of themixture to' float to the surface and flow to tank 59 in .the flotationfoam carried on the water discharged from the cyclone to said tank. Arotary sludge extractor 60 skims the foamy sludge from the surface ofthe water in tank 59 into a discharge launder 6I mounted thereon. Thewater overiiowing from the cyclone separator 51 to the tank 59 isrelatively free of solids of the suspension medium.

A portion of the water from the cyclone separator is bled olf of theline 62 leading t0 tank 59 and passed to a vacuum filter 63 Where it isclaried of all suspension medium. The clarified water from the vacuumfilter is fed to the intermediate set of washing sprays 5I over thescreens 49.

Under the action of centrifugal force in the cyclone separator 51 theparticles of limestone of the suspension medium separate from the waterand gather in the bottom of the cyclone which is closed by a, softrubber pad 64 mounted on the end of a pivoted lever 65 and balanced by acounterT weight 66 adjustable along the other end of the lever. Theposition of the counterweight 66 is adjusted to balance the pressure ofthe liquid and solids above the valve pad 64 until a desired minimumconcentration of solids which it is desired to extract from the cycloneexists above the valve pad. When the concentration of solids 'in thebottom of the cyclone exceeds the desired minimum value for which thecounterweight is set, the pressure above the valve pad overcomes thecounterweight to open the valve and the thickened suspension ilows downinto the high specic gravity tank 61. When the ilow has continued to thepoint where the concentration in the cyclone Vdecreases below thedesired minimum, the counterweight will close the valve 64 and the flowwill be cut oil'` until the concentration again builds up. Thus the tank61 is kept supplied with concentrated suspension from the cyclone.

Concentrated suspension from the tank 61 flows through pipe 68, equippedwith a regulating valve 89, to a mixing tank 18 where it is mixed withwater supplied through pipe 1i equipped with a regulating valve 12, fromwater tank 59. From the mixing tank 18 the reformed suspension medium ofdesired specic gravity is pumped through pipe 19 by pump 14 to the mainseparating tank 5 to maintain the level of medium therein and to insuremaintenance therein of the proper concentration of the suspensionmedium.

'I'he delivery of concentrated suspension and water to the mixing tank18 is regulated so as to maintain at a constant predetermined value thespecific gravity of the suspension therein which is fed to the maintreatment tank 5. This regulation is eilected by a specific gravitycontrol system generally designated 15. This system includes a container16 which is constantly supplied with suspension bled oil of the feedpipe 13 at 11. The container is provided with a small drainage opening18 in the bottom thereof and an overilow 19 at the top so as to maintaina constant level of suspension medium in the container 16 and-preventbuilding up the concentration therein.

A pipe 88, bent to U-shape, is immersed in the suspension in the tank 16so that its horizontal portion 8| is about 50 inches below the level ofthe suspension. A series of small holes 82 are provided in the lowerside of the immersed horizontal portion 8| of the U-shaped pipe. One end83 of the pipe 88 is connected to a diaphragm pressure gauge 84 and theother end 85 is connected to a constant pressure air tank 86 which issupplied with compressed air from` a supply pipe 81 through a reducingvalve 88 which is set to maintaina constant pressure of 100" W. G. inthe l tank 86. A series of small oriilces 89 in the connection from thetank 86 to the U-shaped pipe 88 provides for low volume feed of air atconstant pressure to the Pipe. i

The pressure of air in pipe 88 is always lower than 108" W. G. becauseair is fed through orices 89 ata very slow rate and as soon as thepressure in pipe 88 reaches the value corresponding to the head ofsuspension above holes 82, the air escapes through those holes andbubbles up .3 the surface of the bath. As a result, the pressure insidepipe 88 is always equal to that created by the height h (in inches) vofsuspension existing above the level of holes 82, or: P=h S where S isthe specific gravity oi' the bath. As h is kept constant, pressure Pdirectly measures the speciilc gravity of the suspension in the mixingtank 18. The pressure in the pipe 88 is registered by diaphragmpressure-gauge 84, which may also be made into a recorder if it isdesired to keep a close check on the operation of the treatment tank.

The gauge 84 controls the speciilc gravity in mixing tank 18 in anautomatic manner. When the specific gravity increases above the desiredvalue, for which the diaphragm is kept at its average position by anadjustable spring 98, the diaphragm is lifted, and through a set oflight arms and rods 9| tilts to the left mercury switch 92, therebystarting electric motor 93 which through arm 94, link 95 and lever 96 onvalve shaft 91 operates valves 69 and 12 from position #l to position#21. Valve 12, now fully open, admits more water from tank 59 to themixing tank, while valve 69 which controls the flow of heavy suspensionfrom tank 61 is nearly closed. Thus the specific gravity of thesuspension in the mixing tank is quickly reduced. As soon as thespeciflc gravity is back to normal, the spring pulls the diaphragm backand so throws open the switch 92, thereby `deenergizing motor 93. Valves6-9 and 12 then are brought back to position 1 by counterweight 98 onlever 96 and from then on 4deliver a greater proportion oi' heavysuspension than water to the mixing tank, thus tending to increase thespecific gravity. By this means, the speciiic gravity of the suspensionin tank 18 will continually fluctuate within very narrow limits aroundthe desired value, withoutever exceeding those limits. For instance, forcoal-washing, if a gravity of 1.50 is desired, the range 'of variationswill be from 1.49 to 1.51, which amounts to keeping an average of 1.50.

All of the tanks 54, 59, 61 and 18 are provided with agitators 99 toprevent settling out of the solids suspended in the liquids maintainedin or passing through the tanks. Make-up limestone dust of the propernneness is fed to the tank 61 by a feeder |88 to replace the smallamount inevitably carried oil' with the separated materials and cleanmake-up water is supplied to the nal wash spray 52.

While a preferred process and apparatus for use in practicing the samehas been described and shown by way of illustration, it will beunderstood that various modifications in the details thereof may beresorted to without. departing from the spirit oi the invention withinthe scope of the appended claims.

I claim: I

1. The process of separating a mixture of light, intermediate and heavysolid particles into its components according to their speciiicgravitis, which comprises introducing the mixture into a body ofsuspension medium comprising finely ground solid particles in water,maintaining the suspension medium at a density to float only the lightparticles of the mixture whereby the interl mediate and heavy particlestend to fall by gravity in a downward path through the suspensionmedium, imparting a sidewise propelling movement to the heavy particlesacross the line of their gravitational path, at a zone in said body ofsuspension medium intermediate the top and bottom thereof, toward oneside of said body, while avoiding creation of vertical currents in thesuspension and While simultaneously permitting the intermediateparticles to move by gravity below suchl zone of sidewise propellingmovement, segregating the so-propelled heavy particles at said side ofthe body of suspension medium and thereafter removing them -irom saidbody, and removing the intermediate particles from the body ofsuspension medium at a location below that at which said heavy particlesare segregated.

2. The process of separating light particles, intermediate particles andheavy particles from each other in a mixture thereof in the presence ofa medium comprising a suspension of finely divided solid particles inliquid, which comprises maintaining a body of the medium at a density tofloat the light particles only whereby the intermediate and heavyparticles fall by gravity through said suspension medium at varyingrates of/speed, feeding the mixture to the upper part of said body ofsuspension medium, removing floated light particles from the surface ofthe suspension medium, permitting the intermediate and heavy particlesto fall by gravity in a downward path through the suspension meduim, ata zone in said body of suspension meduim intermediate the top and bottomthereof, imparting -to the heavy particles only a sidewise step-bysteptranslational movement to one side of said body of suspension mediumwhile simultaneously permitting the intermediate particles to progressby gravity past such zone of translational movement, segregating heavyparticles at said side thereof, and thereafter removing them from saidbody of suspension medium, and removing intermediate particles from saidbody of suspension medium at a location below that at which said heavyparticles are withdrawn.

3. The process of separating light particles, intermediate particles andheavy particles from each other in a mixture thereof in the presence ofa medium comprising a suspension of nely divided solid particles inliquid, which comprises maintaining a 4body of the medium at a densityto float the light particles and nearly to float the intermediateparticles, feeding the mixture to the upper part of said body ofsuspension medium, removing oated light particles from the surface ofthe suspension medium, permitting the intermediate and heavy particlesto fall by gravity in a downward path through the suspension medium, ata zone in said body of suspension medium intermediate the top and bottomthereof, imparting to the heavy particles only a sidewise step-by-steptranslational movement to one side of said body of suspension mediumwhile simultaneously permitting the intermediate particles to progressby gravity past such zone of translational movement, segregating heavyparticles at said side thereof,- and thereafter removing thm from saidbody of suspension medium, diverting the intermediate particles along adownwardly inclined path toward another side of said body of suspensionmedium than that to which the heavy particles are moved, and removingintermediate particles from said body of suspension medium at--saidother side of the latter and at a location below that at which saidheavy particles are withdrawn.

4. In apparatus for separating mixtures of solid materials of differentspecific gravities by theA oat-and-sink method involving use of asuspension medium essentially consisting of a suspension of finelydivided solid material in a liquid and having a density adapted to oatone but not all of the constituents of the mixture to be separated, atank containing a body of such suspension medium, a sloping deck mountedwithin the lower portion of said tank and having a stepped surfaceproviding spaced shoulders facing the higher end thereof, means formounting said deck for a reciprocating motion substantially in the planethereof, means for reciprocating said deck with a differential motion inwhich said deck is moved faster toward the lower end than toward thehigher end thereof, means for removing heavy material progressing overthe` higher end of said deck, means for removing intermediate materialgravitating toward the lower end of the said deck, and means forremoving light material iioated on the surface of the suspension mediumin the tank.

5. In apparatus for separating mixtures of solid materials of differentspecific gravities by the oat-and-sink method involving use of asuspension medium essentially consisting of a suspension of finelydivided solid material in a liquid and having a density adapted to floatone but not all of the constituents of the mixture to be separated, atank containing a body of such suspension medium, a sloping deck mountedwithin said tank beneath the surface of such body of suspension mediumfor reciprocation substantially in lts own plane, said deck having astepped surface providing spaced shoulders facing the higher endthereof, means for imparting reciprocating motion to said deck, andseparate means for removing separated materials adjacent the higher andthe lower ends of the deck.

6. In apparatus for separating mixtures of solidv materials according tospecific gravity wherein the materials are separated by selective actionof a suspension medium of iinely divided solid in liquid in a separatingtank and wherein separated materials are washed to remove suspensionmedium therefrom and the wash waters are clarified to produce a supplyof thickened suspension medium and water, and thickened suspensionmedium and water are mixed in regulated quantity to form a suspensionmedium of desired specific gravity for replenishing the supply in thetank, a mixing tank, means for delivering reformed suspension medium ofdesired specific gravity from the mixing tank to the separating tank, acontrol receptacle, means for continuously passing a portion of reformedsuspension medium from said mixing tank to said control receptacle tomaintain a constantlevel of suspension medium therein, a U-shaped pipeimmersed in said control receptacle having perforations below the levelof medium therein and connected at one end to a pressure responsivemeans, means for supplying air under constant pressure to said pipethrough the end thereof opposite to that connected to said pressureresponsive means, and means under control of said pressure responsivemeans for controlling the feed of thickened medium and liquid to saidmixture tank.

7. The process of separating light particles, intermediate particles andcoarse and fine heavy particles from each other in a, mixture thereof inthe presence of a medium comprising a suspension of finely divided solidparticles in liquid, which comprises maintaining a bath of the medium ata density to float the light particles and nearly to float theintermediate particles, feeding the mixture into said bath of suspensionmedium, removing floated light particles from the surface of the bath ofsuspension medium, permitting the intermediate and heavy particles tofall by gravity in a downward path through the suspension medium atvarying rates of speed, at a zone in said body of suspensionintermediate the top and bottom thereof, imparting to the coarse heavyparticles only a sidewise step-bystep translational movement to one sideof said body of suspension medium, while permitting the body andthereafter removing them from the latn ter, withdrawing suspensionmedium and associated fine heavy particles from the bottom of said bath,and separating tine heavy particles from the withdrawn suspensionmedium.

8. Apparatus for separating a ,mixture of solid materials of differentspecific gravities according to the fioat-and-sink method involving theuse a liquid which suspension medium is maintained at such a densitythat at least one but not al! of the constituents of the mixture sinkstherein. which comprises in combination a separating tank containing abody of such suspension medium, means for delivering the mixture to beseparated to the upper part of the body of suspension medium, a-slopingdeck mounted within said tank for reci'procation substantially in itsown plane. said deck having a stepped upper surface providing spacedshoulders facing the higher of a suspension medium essentiallyconsisting of zo a suspension oi iinely divided solid material in endthereof, means mounted in said tank above said deck for divertingsinking particles onto said deck, means for imparting reciprocatingmotion to said deck, segregating channels associated with the higher andlower ends of said deck to receive materials discharged over said ends,and separate means for withdrawing segregated materials from saidsegregating channels.

JEAN ALBERT BRUSSET.

